The invention relates in general to assembly systems and in particular to a new and useful device for the automatic conveyance of tentering frames between a waiting station, especially for the welding of loosely joined automobile carriage parts, the tentering frames being displaceable parallel to a workpiece transfer line on guiding rails, extending cross-wise to the transfer line and out of a sliding position into a working position.
Such tentering frames are used especially in the mass production of automobile carriages. The frames hold provisionally joined construction groups of the raw carriage, for example bottom-, roof-, or side pieces or parts which are supplied along the transfer line and centered, so that an automatic welding of the entire carriage can be carried out. Through German patent No. 28 10 822 it is known, to assemble two different construction types of raw carriages in one common transfer line and to weld them. For this purpose there is for each construction type a corresponding set of tentering frames which are brought into a working position by means of a programmed control. A set of tentering frames, which are not in use for the moment thus have to go into a waiting position, so that they cannot hinder each other during the displacing movements.
In the case of this prior art the waiting positions are situated in front of and behind the working position, in relation to a direction which is parallel to the transfer line.
However, in the modern mass production of working pieces, especially of automobile carriages it is supposed, that more than two types of working pieces can be treated in one transfer line. The German patent No. 28 10 822 deals with this requirement insofar, as it provides a magazine of several tentering frames for different types of work pieces and as it provides conveying devices for the working stations for the fetching and bringing back of the suitable tentering frames. Of course such a measure requires a lot of controlling- and operating expense and as a consequence a high need of space.
In the case of the prior art it is possible as well to provide further waiting stations apart from the waiting station, in order to place there two tentering frames for different working piece types. However, such a measure enlarges the need in space for the entire device for treating the work pieces, and thus show substantial disadvantages.
It is known from the German patent mentioned, to dispose three tentering frames for different construction types in the area of a working station at both sides of the transfer line. This measure, however, supposes first, that the upper edges of the tentering frames are disposed twistable at a rotating body, the axis of which is disposed parallel to the transfer line and extends far above the work piece to be treated. The lower edges of the tentering frames are held in linear guidings and thus can be put up against the work piece to be treated by a pivoting movement of the guidings. Such a measure necessitates a considerable need in space above the transfer line as well as a rugged scaffolding construction for the guiding of the tentering frames.